The present invention relates generally to providing network services such as load balancing, packet filtering or Network Address Translation (NAT). More specifically, network services are provided using service managers that are integrated into a routing infrastructure.
As the IP protocol has continued to be in widespread use, a plethora of network service appliances have evolved for the purpose of providing certain network services not included in the protocol and therefore not provided by standard IP routers. Such services include NAT, statistics gathering, load balancing, proxying, intrusion detection, and numerous other security services. In general, such service appliances must be inserted in a network at a physical location where the appliance will intercept all flows of interest for the purpose of making its service available.
FIG. 1 is a block diagram illustrating a prior art system for providing a network service. A group of clients 101, 102, and 103 are connected by a network 110 to a group of servers 121, 122, 123, and 124. A network service appliance 130 is physically located in the path between the clients and the servers. Network service appliance 130 provides a service by filtering packets, sending packets to specific destinations, or, in some cases, modifying the contents of packets. An example of such modification would be modifying the packet header by changing the source or destination IP address and the source or destination port number.
Network service appliance 130 provides a network service such as load balancing, caching, or security services. In providing security services, network service appliance 130 may function as a proxy, a firewall, or an intrusion detection device. For purposes of this specification, a network service appliance that acts as a load balancer will be described in detail. It should be noted that the architecture and methods described are equally applicable to a network service appliance that is functioning as one of the other above described devices.
Network service appliance 130 is physically located between the group of servers and the clients that they serve. There are several disadvantages to this arrangement. First, it is difficult to add additional network service appliances when the first network service appliance becomes overloaded because the physical connections of the network must be rerouted. Likewise, it is difficult to replace the network service appliance with a back up network service appliance when it fails. Since all packets pass through the network service appliance on the way to the servers, the failure of the network service appliance may prevent any packets from reaching the servers and any packets from being sent by the servers. Such a single point of failure is undesirable. Furthermore, as networks and internetworks have become increasingly complex, multiple services may be required for a single network and inserting a large number of network service appliances into a network in places where they can intercept all relevant packet flows may be impractical.
The servers may also be referred to as hosts and the group of servers may also be referred to as a cluster of hosts. If the group of servers has a common IP address, that IP address may be referred to as a virtual IP address (VIPA) or a cluster address. Also, it should be noted that the terms client and server are used herein in a general sense to refer to devices that generally request information or services (clients) and devices that generally provide services or information (servers). In each example given it should be noted that the roles of client and server may be reversed if desired for a particular application.
A system that addresses the scalability issues that are faced by network service appliances (load balancers, firewalls, etc.) is needed. It would be useful to distribute functions that are traditionally performed by a single network element and so that as much function as possible can be performed by multiple network elements. A method of coordinating work between the distributed functions with a minimum of overhead is needed.
Although network service appliances have facilitated the development of scalable server architectures, the problem of scaling network service appliances themselves and distributing their functionality across multiple platforms has been largely ignored. Network service appliances traditionally have been implemented on a single platform that must be physically located at a specific point in the network for its service to be provided.
For example, clustering of servers has been practiced in this manner. Clustering has achieved scalability for servers. Traditional multiprocessor systems have relatively low scalability limits due to contention for shared memory and I/O. Clustered machines, on the other hand, can scale farther in that the workload for any particular user is bound to a particular machine and far less sharing is needed. Clustering has also facilitated non-disruptive growth. When workloads grow beyond the capacity of a single machine, the traditional approach is to replace it with a larger machine or, if possible, add additional processors within the machine. In either case, this requires downtime for the entire machine. With clustering, machines can be added to the cluster without disrupting work that is executing on the other machines. When the new machine comes online, new work can start to migrate to that machine, thus reducing the load on the pre-existing machines.
Clustering has also provided load balancing among servers. Spreading users across multiple independent systems can result in wasted capacity on some systems while others are overloaded. By employing load balancing within a cluster of systems the users are spread to available systems based on the load on each system. Clustering also has been used to enable systems to be continuously available. Individual application instances or machines can fail (or be taken down for maintenance) without shutting down service to end-users. Users on the failed system reconnect and should not be aware that they are using an alternate image. Users on the other systems are completely unaffected except for the additional load caused by services provided to some portion of the users that were formerly on the failed system.
In order to take full advantage of these features, the network access must likewise be scalable and highly available. Network service appliances (load-balancing appliances being one such example) must be able to function without introducing their own scaling limitations that would restrict the throughput of the cluster. A new method of providing network services using a distributed architecture is needed to achieve this.
When network services are provided using a distributed architecture, it is important that the distributed system be able to gather statistics. Furthermore it is desirable that such gathering of statistics be accomplished in a general fashion that works for all services provided and is not application-specific. However, it is difficult to define a generalized scheme for all packet services since the statistics to be gathered such as byte and packet counts tend to depend on the specific services being managed. Certain statistics may not be of value for all applications and may in fact be misleading if presented for the wrong applications. A generalized scheme is needed that allows flexibility to indicate the statistics that are of value for particular applications and that still maintains generality for a variety of applications.
A generalized scheme whereby service managers and forwarding agents provide services and gather statistics about packets being serviced is disclosed. Fixed affinities are sent that identify flows for which statistics are to be kept and also assist in controlling packet forwarding. Thus, for each flow that is being serviced, the service manager can define a statistics gathering policy that is tailored to the flow. The forwarding agents need not be programmed separately to gather statistics in a certain way or in different ways for different applications. The forwarding agents need only be programmed to follow the instructions included in fixed affinities that identify certain flows. Service managers may specify statistics to be gathered for different applications and forwarding agents are configured to gather statistics according to those instructions.
It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, a method, or a computer readable medium such as a computer readable storage medium or a computer network wherein program instructions are sent over optical or electronic communication links. Several inventive embodiments of the present invention are described below.
In one embodiment, a method of gathering statistics about packets includes determining at a service manager statistics that are to be gathered for a flow and sending instructions to a forwarding agent from the service manager detailing how to gather statistics for the flow. The forwarding agent is implemented on a network device and the forwarding agent is operative to receive statistics gathering instructions for a flow from the service manager. A report is received at the service manager of statistics gathered at the forwarding agent according to the instructions sent by the service manager.
In another embodiment, a forwarding agent includes a service manager receiving interface for receiving instructions from a service manager specifying statistics to be gathered for server designated packets. A network packet receiving interface receives IP packets from a network. A processor gathers statistics for the server designated packets. A memory stores the statistics and a sending interface sends statistics to a statistics collector.
In another embodiment, a service manager includes a processor configured to determine statistics that are to be gathered for a flow. A forwarding agent sending interface is configured to send instructions to a forwarding agent from the service manager detailing how to gather statistics for the flow. The forwarding agent is implemented on a network device and the forwarding agent is operative to receive statistics gathering instructions for a flow from the service manager. A forwarding agent receiving interface is configured to receive a report at the service manager of statistics gathered at the forwarding agent according to the instructions sent by the service manager.
These and other features and advantages of the present invention will be presented in more detail in the following specification of the invention and the accompanying figures which illustrate by way of example the principles of the invention.